In a cellular wireless communication system, such as a code division multiple access (CDMA) system for instance, base stations are positioned throughout a coverage area and emit radio frequency radiation patterns that define cells. Mobile stations operating in a given cell may then wirelessly communicate with the serving base station, and the base station may provide connectivity with further network components such as switches and gateways that connect with transport networks.
In a CDMA system, each cell is typically divided into a number of sectors, each of which is identified by a specific pseudo-noise offset (i.e., “PN offset”) of a specific spreading sequence that is used to encode communications with mobile stations operating in the cell. At any given instant, a mobile station may thus operate in a given sector, and may thereby communicate with the serving base station using the PN offset of that sector. (In practice, an idle mobile station may communicate on a single PN offset (i.e., in a single sector) at once; an active mobile, on the other hand, might communicate on multiple PN offsets (i.e., in multiple sectors) at once, although a dominant one of those active PN offsets might be the focus of communications at any given moment.)
Unfortunately, in some wireless networks, the cells may not seamlessly cover an entire area, so there may be a hole in coverage between cells. To solve this problem, a wireless carrier may install a repeater that functions to extend the range of a given cell or sector, so as to fill in the hole in coverage. Such a repeater may be able to receive a signal distorted by transmission losses and to regenerate or replicate the signal. The repeater typically includes a donor antenna that communicates with a base station, a coverage antenna that communicates with mobile stations, and an amplifier circuit that boosts communications from the base station to the mobile stations as well as from the mobile stations to the base stations. For example, the repeater may be positioned between a mobile station and a base station to intercept signals sent between them. The repeater amplifies the power of these intercepted signals and sends amplified versions of these signals to the mobile station or the base station. Therefore, the repeater effectively extends the range of a given cell by boosting communications between a mobile station and a base station.
In practice, the donor antenna of a repeater may receive signals from multiple base stations and multiple base station sectors (i.e., signals with multiple PN offsets) at once and boost all of those signals. In addition, the repeater receives signals from mobile stations, boosts the signals, and radiates the amplified signals to one or all nearby base stations.
However, radiating the amplified signals to the base stations can decrease the capacity of base stations because it raises the noise level received by the base station. The increase in noise levels reduces the signal-to-noise ratio of the signals received by the base station. The noise is typically thermal noise generated from active devices in the repeater, and if it reaches the receiver of a base station transceiver at a high enough power level, the receiver will be desensitized causing loss of coverage area.